1. Field of the Invention
The invention is directed to a catalytic reactor. For endothermic reactions. Examples of such reactions are the production of hydrogen by steam reformation of hydrocarbons and dehydrogenation processes that are carried out, e.g., for the production of styrene from ethylbenzene or of propylene from isobutane.
2. Description of the Prior Art
A catalytic reactor having an external cylindrical shape and a reaction chamber with a circular cross section is known from EP 0 380 192 B1. The input material to be catalyzed is introduced from the bottom into the reaction chamber which is filled with a catalytic material, while the obtained catalytically converted product is extracted from the upper end of the reaction chamber. This known reactor is heatable by means of a burner which is arranged below the base level of the reaction chamber and enclosed in the region of its combustion zone by a refractory shell. The flame direction of the burner is oriented coaxially to the longitudinal direction of the reaction chamber. The ascending combustion gases of the burner are guided along virtually the entire length of the reaction chamber in a heat distributor which is formed as a tubular body from a material with good heat conduction and directly adjoins the refractory combustion chamber wall. An annular gap remains open between the tubular heat distributor and the inner defining wall of the annular reaction chamber. The occurring hot combustion gases are therefore first guided upward by the heat distributor and are deflected into the annular gap at the upper end of the heat distributor. The combustion gases then flow downward through the annular gap and, in so doing, give off heat into the reaction space through the inner defining wall. At the same time, however, the combustion gases flowing downward past the wall of the heat distributor also absorb heat from the hot combustion gases flowing upward in the interior of the heat distributor so that the temperature of the gases in the annular gap remains virtually constant. In this way, the known device can be operated as an isothermal reactor in practice.
In another embodiment form, the reactor known from EP 0 380 192 B1 has a plurality of parallel heat distributors arranged in place of a central heat distributor. There is also only one burner provided in this device, this burner being arranged with its combustion space below the base level of the reaction chamber. Since practically no heat is given off externally in the combustion space itself, the combustion of the fuel used in each case takes place under adiabatic conditions so that, depending on the fuel, undesirably high flame temperatures are reached. In order to decrease the temperature of the combustion gases, the conventional amount of approximately 10% excess air can be considerably increased, e.g., to 50%. However, this leads to a compulsory corresponding increase in the amount of exhaust gas with the consequent heat losses, which is also undesirable. As an alternative to a reduction in temperature, EP 0 380 192 B1 proposes a return of exhaust gas to the combustion zone. This has the particular disadvantage of additional construction costs.
Another endothermic reactor is known from EP 0 369 556 B1. The reaction chamber of this reactor, which is filled with a catalyst, is designed as a tubular shell or sheathing tube which is closed at the bottom end. An ascending pipe is inserted into the latter in such a way that the material to be processed can flow in opposite directions through the annular space between the sheathing pipe and the ascending pipe, on the one hand, and through the ascending pipe, on the other hand, in order to pass the reaction space. In this apparatus, the hot combustion gas for heating the reaction space is generated in a separate part of the installation under adiabatic conditions and is subsequently introduced laterally into the refractory housing in the lower end region of the reaction space, this housing enclosing the reactor externally at a distance. In order to prevent hot combustion gas from striking the wall of the reaction space directly and causing damage as a result of the high temperature, the combustion gas is fed in the housing in such a way that the hot gases first strike a tubular barrier of refractory material, are deflected upward, and guided down again from the upper end of the refractory barrier along a second tubular barrier formed of a material with good heat conducting properties. The combustion gas can only flow up again at the bottom end of the second barrier and come into a heat-exchanging contact with the wall of the reaction space. At the same time, heat transfer takes place between the combustion gases flowing in opposite directions through the heat conducting wall of the second barrier. As in the device known from EP 0 380 192 B1, these steps bring about an appreciable reduction in the temperature of the combustion gas so that the wall of the reaction chamber is protected from impermissible thermal loading. The reaction space of this reactor is limited to a single reactor vessel so that the reactor vessels in installations having different output capacities must be provided with new dimensions as appropriate. Further, it is disadvantageous that the barriers which are exposed to high temperatures have closing or sealing parts which must be exchanged after a certain period of operation.